In recent years, incidence of diabetes has been displaying an upward trend every year. In Japan alone, a combined number of diabetics and potential diabetics is estimated to be ten million or more. Also due to a very high interest in lifestyle-related diseases, opportunities to self-manage blood sugar levels have been increasing. In response to such recent trend, it is important to develop technologies for self-measuring and managing blood sugar levels. Although many blood sugar measuring technologies have been put to practical use, electrochemical sensing is useful from the standpoints such as scaling down the amount of sample to a minute quantity, shortening a measuring time, and reducing the size of a device.
Enzymes whose substrate is glucose that exist in blood are utilized in a technique for sensing in blood sugar measuring technologies. Examples of such enzyme include glucose oxidase (EC 1.1.3.4). Glucose oxidase is advantageous in that it has a high specificity for glucose and is highly stable against heat. In a blood sugar sensor using glucose oxidase, measurement is performed by transferring, to an electrode via mediator, electrons generated in a process of oxidizing glucose so as to be converted into D-glucono-δ-lactone. However, glucose oxidase easily transfers protons generated in the reaction to blood-dissolved oxygen, which affects a measured value and thus has been problematic.
In order to avoid such a problem, pyrroloquinoline quinone-dependent glucose dehydrogenase (EC 1.1.5.2 (former EC 1.1.99.17)) has been used as an enzyme for blood sugar sensors. Hereinafter, pyrroloquinoline quinone-dependent glucose dehydrogenase is also represented as PQQGDH as appropriate. PQQGDH is advantageous in that it is not affected by the dissolved oxygen. However, PQQGDH has a low substrate specificity and has an activity also toward sugars other than glucose, such as maltose and lactose, and thereby, has been problematic since accurate measurement of glucose is difficult.
Therefore, flavin adenine dinucleotide is gathering attention as a glucose dehydrogenase that is not affected by dissolved oxygen and that has superior substrate specificity. Hereinafter, flavin adenine dinucleotide is represented as FAD as appropriate. Glucose dehydrogenase is represented as GDH as appropriate. Flavin adenine dinucleotide-dependent glucose dehydrogenase is represented as FADGDH. FADGDH is described in Non-patent Literature 1 to 6, and has been known for a long time.
Patent Literature 1 discloses a gene sequence and an amino acid sequence of an FADGDH derived from Aspergillus terreus. Patent Literature 2 discloses an FADGDH derived from Aspergillus oryzae. Patent Literature 3 discloses a modified FADGDH having an improved thermal stability, resulting from modifying an FADGDH derived from Aspergillus oryzae. Patent Literature 4 discloses a modified FADGDH having improved thermal stability and action to xylose, resulting from modifying an FADGDH derived from Aspergillus oryzae and an FADGDH derived from Aspergillus terreus. Patent Literature 5 discloses a glucose sensor using an FADGDH derived from Aspergillus terreus. 
On the other hand, Non-patent Literature 7 indicates that, as a caution for SMBG (Self Monitoring Blood Glucose) devices, measured values obtained from many devices deviate from an acceptable range defined by ISO15197 in an environmental temperature condition such as in a low temperature range and a high temperature range, and may become a cause of medical accidents if the measured values show an extremely low value or a high value.